Walls of the vasculature, particularly arterial walls, may develop areas of pathological dilatation called aneurysms. As is well known, aneurysms have thin, weak walls that are prone to rupturing. Aneurysms can be the result of the vessel wall being weakened by disease, injury, or a congenital abnormality. Aneurysms could be found in different parts of the body, and the most common are abdominal aortic aneurysms and brain or cerebral aneurysms in the neurovasculature. When the weakened wall of an aneurysm ruptures, it can result in death, especially if it is a cerebral aneurysm that ruptures.
Neurovascular or cerebral aneurysms affect about 5% of the population. Aneurysms may be located, for example, along arterial side walls (e.g., the aneurysm 10 illustrated in FIG. 1) and at arterial bifurcations (e.g., the aneurysm 20 illustrated in FIG. 2). The direction of fluid flow is generally indicated by the arrows 16, 26. The aneurysms 10, 20 each have a fundus 12, 22, a neck 14, 24, and a fundus-to-neck ratio or “neck ratio.” If the neck ratio is greater than 2 to 1 or if the neck 14, 24 is less than 4 mm, the aneurysm 10, 20 may be treated with embolization coils alone because the coils will generally constrain themselves within the aneurysm 10, 20 without herniating, or being dislodged from the aneurysm, into parent vessels. If the neck ratio is less than 2 to 1 or if the neck 14, 24 is greater than 4 mm, the aneurysms 10, 20 may be difficult to treat with embolization coils alone because the coils may be prone to herniating into parent vessels, as illustrated in FIG. 3A and FIG. 3B. Herniation of coils may cause arterial occlusion, stroke, and/or death. Compared to the bifurcation illustrated in FIG. 2, the efferent vessels of the bifurcation may be at substantially different angles, have substantially different sizes, and/or be a different quantity (e.g., three or more). Compared to the bifurcation illustrated in FIG. 2, the aneurysm 20 of the bifurcation may be offset with respect to the junction (e.g., having a neck substantially open to one efferent vessel), tilted with respect to a plane created by the vessels (e.g., into or out of the page), etc. Moreover, vasculature may include more than two efferent vessels (e.g., three efferent vessels in a trifurcation). Each of these would still be accurately characterized as a “bifurcation” herein.
In order to inhibit such herniation, tubular neck remodeling devices, for example Neuroform®, available from Boston Scientific, and Enterprise™, available from Cordis Neurovascular, may be used to keep coils or other materials within the fundus of the aneurysm and out of the vessels. Tubular remodeling devices generally consist of a braided wire or cut metallic stent or stents covering the neck of the aneurysm so that materials introduced into the fundus of the aneurysm do not herniate out of the aneurysm. As illustrated in FIG. 4A, tubular remodeling devices 40 are generally useful for side wall aneurysms 10. As illustrated in FIG. 4B and FIG. 4C, tubular remodeling devices 42, 44 are generally less useful for aneurysms 20 at bifurcations (e.g., the basilar tip area), for example because positioning/shaping the remodeling devices to preserve blood flow through the afferent and efferent vessels while also inhibiting herniation of coils 28 out of the aneurysm 20 can be difficult.